Study On The Development Law Of Bidirectional Freezing Temperature Field Of Shield Tunneling In Seabed Removal Under Seepage Conditions

With the continuous development of urban rail transit construction in Linhai and Linjiang,shield machines are more and more "trapped" at the bottom of the sea and river due to the severe wear and tear of cutting tools.Freezing method has become the preferred method for shield tunneling under complex conditions because of its safety,controllability,wide application range and no influence on shield tunneling after thawing.At present,there are few studies on the temperature field of two-way freezing in stages under seepage at home and abroad.Based on the background of Xiamen Metro Line 3 shield machine’s seabed two-way freezing project,this paper studies the development law of the temperature field of seabed shield machine’s two-way freezing under seepage condition through the combination of indoor test,three-dimensional numerical simulation,model test and field measurement.The main contents and achievements of this paper are as follows:(1)The basic physical parameters,thermophysical parameters and mechanical parameters of the frozen stratum are obtained through laboratory tests.The results of particle size distribution of gravel stratum indicate that the gravel stratum belongs to medium-coarse sand stratum.(2)A three-dimensional finite element model of two-way freezing in stages under seepage conditions is established.Firstly,the development laws of horizontal freezing,vertical freezing and bidirectional freezing temperature field under typical parameters are studied respectively.Secondly,the influence laws of initial groundwater flow velocity,initial ground temperature,vertical freezing pipe row spacing,ventilation volume per unit time,brine temperature,vertical freezing pipe diameter and horizontal freezing pipe diameter on freezing temperature field are studied by single factor analysis.The influence of various factors on the freezing temperature field is analyzed.The results show that the existence of shield has great influence on seepage field,the maximum seepage velocity is about 3.2 times of the original seepage velocity;vertical freezing has great influence on the development of horizontal freezing temperature field,while horizontal freezing has little influence on vertical freezing temperature field;group hole freezing can effectively reduce the influence of seepage on its temperature field;the introduction of non-uniform coefficient Kt of temperature distribution on freezing wall can be better.The initial ground temperature,brine temperature and groundwater flow velocity have great influence on the temperature field of freezing curtain,while the ventilation rate per unit time only has great influence on the temperature field of near horizontal freezing,and has little effect on the vertical freezing temperature field.(3)Based on the similarity theory,a two-way freezing model test under seepage conditionis designed and carried out.The results show that the temperature drop of the downstream freezing wall is larger than that of the upstream freezing wall;the thickness of the upstream freezing wall is smaller than that of the downstream freezing wall,and the average temperature of the upstream freezing wall is slightly lower than that of the downstream freezing wall.(4)In-situ measurements of seabed bidirectional freezing under seepage conditions were carried out,and the data of vertical temperature measurement holes at sea and temperature measurement holes at the bottom of shield tunneling were obtained.Through the analysis and study of the data,the results show that the cooling curves and numerical values of each measuring point at different locations of the same temperature measuring hole are basically the same;the opening fire operation has little influence on the whole freezing temperature field,and the temperature of each measuring point has not increased significantly;the two-way freezing scheme has achieved good results in the submarine shield tunneling,which verifies the feasibility of the freezing scheme in the submarine shield tunneling.。(5)By comparing the results of numerical simulation,model test and field measurement,the reliability of the conclusions obtained by the three research methods is verified.